Subjects working in or living near informal gold mining and processing in southern Peru were studied to determine mercury exposures from two tasks: amalgamation and amalgam smelting. The authors collected 17 airborne and 41 urinary mercury levels. The mean urinary levels were 728 (range: 321-1662) and 113 (45-197) microg/L for working in smelters and living near smelters, respectively. A third group working in amalgamation had a mean 18 microg/L (range 8-37). People living in the mining town but with no mining activities had 8 microg/L (5-10), while a control group outside the town had 4 microg/L (2-6). Mean airborne mercury exposure was 2423 microg/m3 (range 530-4430) during smelting, 30.5 microg/m3 (12-55) during amalgamation, and 12 microg/m3 (3-23) in the mining town. Smelters are highly contaminated with mercury, as are the people living around smelters.